Tapped auxiliary winding for multi-speed operation of electric motor and method therefor

ABSTRACT

A capacitor motor and method is disclosed which utilizes one or more tap points within the auxiliary winding of the motor which can be selectively connectd to a source of AC power via a selector switch for multi-speed operation of the motor.

CROSS REFERENCE TO A RELATED APPLICATION

This is a continuation of copending application Ser. No. 882,443 filedon July 7, 1986, now U.S. Pat. No. 4,737,701 which is acontinuation-in-part of application Ser. No. 489,843, filed Apr. 29,1983, now U.S. Pat. No. 4,486,699.

BACKGROUND OF THE INVENTION

This invention relates tO a multiple speed dynamoelectric machine, andmore particularly to a multiple speed permanent split capacitor (PSC) orother capacitor-run multi-speed induction motor, such as may be utilizedto directly drive a fan mounted on the rotor shaft of the motor.

Generally, in a motor application for use with a direct drive overheadceiling fan or the like, the motor is designed to run at a relativelyslow speed. For example, a multiple-speed overhead ceiling fan motor maybe operated at a maximum speed of about 350 rpm and at a minimum speedof about 50 rpm. These motors generally are multiple pole motors havingeither 12 or 18 poles, as compared to more conventional 2, 4, 6, or 8pole motors. A PSC motor is a capacitor run motor that uses itsauxiliary winding and capacitor continuously, without change in thecapacitance. No starting switch or relay is required to switch out theauxiliary winding of the motor once the motor has attained itsoperational speed. Typically, a PSC motor comprises a main windingadapted to be connected across two AC power lines. An auxiliary windingand a permanent running capacitor are wired in parallel to the mainwinding so that upon energization of the windings, the main winding andthe auxiliary winding are spaced 90 electrical degrees apart. Asquirrel-cage-type rotor is usually utilized in PSC induction motors.

In a number of PSC fan motor applications, it is highly desirable toprovide for multiple speed operation of the fan motor. Speed control ofa PSC motor is typically obtained by adjusting the flux of the motor andthereby changing the slip. As a general rule, pole changing is notutilized with PSC motor applications. There are four basic methods ofchanging the flux of the stator and thereby changing the slip andoperating speed of a PSC motor. A first method of speed control of a PSCmotor utilizes a change of connections of the main windings. Secondly,the voltage impressed on one or both the main and the auxiliary windingmay be changed. Thirdly, an external impedance or capacitance may beplaced in series with the main winding of the motor. And, fourthly,various tapping methods using autotransformers and secondary mainwindings are used.

Looking first at voltage change methods for speed control, these methodstypically employ a simple autotransformer used in conjunction with thePSC motor such that the voltage on both the main winding and theauxiliary circuit (i.e., the permanent capacitor and the auxiliarywinding) is the same at all times, but the actual voltage applied to themain and auxiliary windings is varied depending on the tapping point ofthe autotransformer.

In utilizing voltage changes for speed control purposes, the PSC motoris normally operated at its high speed mode of operation when the fullvoltage of the AC power supply is utilized to energize both the main andauxiliary windings of the motor. For example, in an overhead ceiling fanmotor application using voltage speed control, the full AC line voltage(120 volt) would be impressed across the windings resulting in highspeed operation of the motor (e.g., 350 rpm). For medium speed operationof the motor, the autotransformer in parallel with the main andauxiliary windings is tapped at an intermediate point so as to reducethe voltage impressed on both the main and auxiliary windings with acorresponding speed-torque curve reduction such that the torque of themotor is less than at its high speed operation with the drag or slip ofthe fan blades resulting in a steady state operating speed of the motorslower than its high speed mode of operation. Likewise, slower speedmodes of operation may be obtained by further reducing the voltage (andhence the torque) of the motor. In voltage speed control systems, theoperating speed of the motor generally depends on the load applied tothe motor. Also, the locked rotor torque of the motor is necessarily lowwhen the motor is operated at its low speed mode of operation and thelow speed connection is inherently unstable because the fan-torque andmotor-torque curves intersect one another at a very small angle suchthat the motor is sensitive to changes in voltage and in load.

If an external impedance is utilized for speed control purposes, theimpedance typically is either a resistor or a reactor which is connectedin series with the main winding such that the voltage impressed acrossthe main winding is reduced when the impedance is connected in series tothe main windings thereby reducing the flux and increasing the slip ofthe motor and in turn reducing the operating speed of the motor. In thecoassigned U.S. Pat. No. 4,408,150, a capacitor is interconnected inseries with the main winding of the motor and which, when seriallyconnected to the main winding of the motor, results in a reduction inspeed of the motor.

In tapped winding speed control arrangements, such motors typicallyeffect speed control by flux control, accomplished primarily by changingthe impressed volts per turn on the main winding. Generally, tappedwinding motors vary the volts per turn (and hence the flux, slip, andspeed of the motor) by changing the number of series conductors in themain winding. For example, a two speed tapped winding motor utilizesthree windings including a main winding, an extra main or intermediatemain winding, and an auxiliary winding. The main and intermediate mainwindings are wound in space phase with one another (i.e., one is woundon top of the other) in the same slots, with the same distribution butnot necessarily with the same number of turns or wire size. For morethan two speeds, the intermediate main winding itself is tapped.

In a recently commercially available PSC direct drive fan motor, onlyone main winding was provided and the auxiliary winding was tapped atdifferent locations. Through the use of a double pole, triple throwspeed selector switch, selected physical poles of the auxiliary windingcould be electrically removed from the remainder of the auxiliarywinding in parallel with the main winding, or the tapped auxiliarywinding could be utilized as a voltage divider thereby to change theflux impressed upon the windings of the motor. However, because one ormore of the physical poles of the auxiliary winding of this motor is notenergized at the intermediate or slower speeds of operation of themotor, the flux distribution of this motor is not balanced around thestator core and this unbalanced magnetic flux results in noisy operationof the motor at slower speeds.

SUMMARY OF THE INVENTION

Among the several objects and features of the present invention may benoted the provision of a multi-speed induction motor and method of speedcontrol therefor which enables multiple speed operation of the motor,but yet which does not require the use of autotransformers, externalimpedances, external capacitors, or additional main windings, and yetresults in a balanced flux distribution at all of its operationalspeeds;

The provision of such a motor and method which significantly lessens theamount of magnet wire required for the windings of the motor (as opposedto prior art tapped winding speed control methods using intermediatemain windings);

The provision of such a motor and method which utilizes a single polespeed selector switch thus enabling a motor of the present invention toreplace existing multi-speed motors without the necessity of changingthe switching network;

The provision of such a motor which has a significantly lower slot filland which has windings which are relatively easy to insert in the slotsof the stator core during manufacture;

The provision of such a motor which eliminates the necessity of a fastacting thermal protector switch for protecting the windings of the motoragainst overheating in the event the motor capacitor fails is a shortedcondition; and

The provision of such a motor and method which has a lower productioncost than other multi-speed PSC motors, which is reliable in operation,and which is quiet in operation at all operational speeds.

Briefly stated, a multiple speed electrical induction motor of thepresent invention has a stator core comprising a stack of laminations ofsuitable ferromagnetic material. The core has a central bore extendingtherethrough and a plurality of slots extending generally radiallyoutwardly from the bore. A rotor is rotatably received within the boreand windings are inserted in the stator slots, these windings comprisinga main winding and an auxiliary winding. A capacitor has one sidethereof connected in series with the auxiliary winding. The auxiliarywinding is comprised of a plurality of coil sets with each coil sethaving a plurality of serially connected coils placed in the stator coreslots at substantially equal angular intervals around the central boreof the core so as to constitute the poles of the windings. A first tappoint is provided between the first and second coil sets of theauxiliary winding and a last tap point is provided between the last ofthe coil sets of the auxiliary winding and the main winding. A pair ofpower lines is connected to a source of alternating current power, withone side of the main winding and the other side of the capacitor beingconnected to one side of this power source, and with the auxiliarywinding being connected to the other side of this power source. A speedselector switch is provided having a movable switch arm or member whichis connected to the other side of the main winding, this switch armbeing movable between a high speed position in which a maximum number(e.g., all) of the coil sets of the auxiliary winding is energized inseries with the capacitor, and in which the maximum number of coil setsof the auxiliary winding, the capacitor, and the main winding are inparallel with the other side of the power source such that the motoroperates in its high speed mode of operation. The speed selector switchis further operable in a low speed position in which a minimum number ofcoil sets of the auxiliary winding (e.g., one such auxiliary coil set)is connected in series with the capacitor, and in which the minimumnumber of auxiliary coil sets, the main winding, and the capacitor arein parallel with the other side of the power source such that the motoroperates at a slow speed mode of operation.

Other objects and features of this invention will be in part apparentand in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a portion of an overhead ceilingfan illustrating a multiple speed permanent split capacitor (PSC) motorof the present invention and a speed selector switch with portionsbroken away to show details of construction of the motor and the switch;

FIG. 2 is an end view of a portion of a stator of an 18 pole, 2 speedPSC skein wound motor having a single main winding divided into two mainwinding coil sets and a single auxiliary winding divided into twoauxiliary coil winding sets with the coils of the main and auxiliarycoil sets being inserted into the slots of the stator core in layeredgroups to constitute the physical poles of the motor;

FIG. 3 is a diagrammatic view of the windings shown in FIG. 2, but fromthe opposite end of the stator core shown in FIG. 2;

FIG. 4 is a schematic of the windings shown in FIGS. 2 and 3;

FIG. 5 is a diagrammatic view, similar to FIG. 3, of a stator for a 12pole, 2 speed PSC motor having a single main winding divided into twomain winding coil sets and a single auxiliary winding which is alsodivided into two auxiliary winding coil sets with the coils of the mainand auxiliary coil sets being inserted into the slots of the stator corein layered groups;

FIG. 6 is a schematic of the windings shown in FIG. 5;

FIG. 7 is a diagrammatic view, similar to FIGS. 3 and 5, of a 12 pole, 4speed PSC motor having a single main winding divided into two mainwinding coil sets and a single auxiliary winding divided into fourauxiliary winding coil sets with the coils of the main and auxiliarywindings being inserted into the slots of the stator core in layeredgroups each comprising two main winding coils and four auxiliary windingcoils with a plurality of tapping points for the selective energizationof each of the auxiliary coil subsets.

FIG. 8 is a simple schematic of the windings and leads shown in FIG. 7;

FIG. 9 is a schematic of the motor windings of FIG. 7 more detailed thanFIG. 8 with the auxiliary coil sets shown as four separate auxiliarycoilsets with the tapping points therebetween for connection to a sourceof AC power via a selector switch such that at a high speed switchposition, all of the coil sets of the auxiliary winding are energized inseries with the capacitor and the motor operates at its high speed modeof operation, such that at a low speed switch position, only one of theauxiliary winding coil sets is energized in series with the permanentcapacitor and the other auxiliary coil sets are in series with the mainwindings such that the motor operates at its slow speed mode ofoperation;

FIG. 9A is a still more detailed schematic of FIG. 9 showing that eachof the auxiliary coil subsets has a number of (e.g., six) seriallyconnected coils therein which are uniformly distributed around thestator core at generally equal angular intervals so as to result inbalanced running of the motor at any of its selected operating speeds;

FIG. 10 is a schematic similar to FIG. 9 of the motor windings shown inFIG. 7, but with the selector switch connected to the auxiliary windingcoil sets in a different manner than is shown in FIG. 9:

FIG. 10A is a more detailed schematic of FIG. 10;

FIG. 11 is a schematic similar to FIGS. 9 and 10 of the motor windingshown in FIG. 7, but with the selector switch connected to the auxiliarywinding coil sets in still a different manner;

FIG. 11A is a more detailed schematic of FIG. 11;

FIG. 12 is a schematic of a typical prior art PSC four speed motorhaving a first main winding, an auxiliary winding connected in parallelto the first main winding with a capacitor therebetween, and threeintermediate or booster main windings in series with the first mainwinding, these intermediate main windings being selectively connectableto the first main winding thereby to progressively slow down theoperating speed of the motor as more of the intermediate main windingsare serially connected to the first main winding;

FIG. 13 is a schematic of a four speed PSC motor of the presentinvention in which the auxiliary winding is divided into four coil setseach having a plurality of coils which are uniformly distributed aroundthe stator core so that with the speed selector switch in its high speedposition, all of the auxiliary winding coil sets are in series with thecapacitor and in parallel connection with the main winding, and suchthat with the speed selector switch in one of its intermediate or slowspeed mode of operation, one or more of the auxiliary winding coil setsis in series connection with the capacitor and parallel to the mainwinding and such that the other auxiliary winding coil sets are inseries connection with the main winding such that the motor operates ata slower speed mode of operation; and

FIG. 14 is a diagrammatic view of still another embodiment of thewindings of a motor of the present invention.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, and particularly to FIG. 1, adynamoelectric machine of the present invention is indicated in itsentirety by reference character 1. Specifically, this dynamoelectricmachine is shown to be a multiple-pole, multiple-speed permanent splitcapacitor (PSC) induction motor. While the motor 1 utilizing the speedcontrol system, construction and method of the present invention isherein described as a PSC motor, those skilled in the art willappreciate that this invention will have applications in other types ofmotors (e.g., other capacitor run motors) and that the multiple-pole(e.g., 12 and 18 pole) motors herein described may have significantlyfewer poles.

More specifically, motor 1 has a stator assembly 3. The stator iscomprised of a core 5 made up of a stack of laminations of suitableferromagnetic material. The core 5 has a central bore 9 extendinglongitudinally therethrough with a plurality (e.g., thirty six) slots 11extending radially outwardly from central bore 9 and with a plurality ofteeth 13 separating the slots. As shown in FIG. 2, core 5 has thirty-sixslots 11 formed therein (as indicated by slots S1-S36) with a respectivetooth 13 (as indicated by T1-T36) between each of the slots.

Motor 1 further includes windings, as generally indicated at W, whichare inserted into slots 11 with these windings having end turns Eextending out beyond the end faces of core 7, as shown in FIGS. 1 and 2.The motor further includes a rotor assembly, as generally indicated at15, having a squirrel cage rotor body (not shown) which in turn has ahollow rotor shaft 17 extending endwise from the motor and with therotor shaft being rotatable with the rotor body. The stator assembly 3further includes a housing or shell 19 surrounding core 5 and extendingout beyond the end turns E of the windings W. An end shield 21 is boltedto each end of the core 5 and to shell 19 and has a bearing support (notshown) formed therein for receiving a ball bearing or the like (also notshown) which in turn receives and journals rotor shaft 17 thereby toaccurately, rotatably support the rotor assembly 15 within central bore9 of stator assembly 3. On the portion of rotor shaft 17 extendingendwise beyond end shield 21, a hub 23 is locked to the rotor shaft soas to be rotatable with the rotor shaft. In an overhead ceiling fanapplication, the paddle fan blades (not shown) of the overhead ceilingfan may be affixed to hub 23 such that the fan blades rotate with therotor shaft 17.

As previously indicated, rotor shaft 17 is a hollow tubular member andit has a wireway 25 extending axially therethrough, this wireway beingstationary with respect to the rotor shaft. A nut 27 is threaded ontothe free end of wireway 25 and this nut holds a switch housing 29 inplace on the lower end of the wireway. The wireway 25 is a tubularrod-like member and serves as a conduit through which various lead wires31 are run to a multiple position speed selector switch, as generallyindicated at 33, located within switch housing 29. In accordance withthis invention, selector switch 33 may be a single pole, multiple throwswitch having a switch arm SA operated by means of a pull chain 35 so asto selectively operate motor 1 at any one of a multiplicity of operatingspeeds. The lead wires 31 extend longitudinally through wireway 25 tothe opposite end of the motor from that shown in FIG. 1 and the variouslead wires are connected to an alternating current power source by powersupply leads Pl, P2 for supplying AC electrical power to selectedportions of the windings W of the motor in accordance with the apparatusand method of this invention, as will be more particularly pointed outhereinafter.

Referring now to a more detailed description of windings W of motor 1,in general, the windings of a motor in accordance with the instantinvention comprises a main winding, as generally indicated at M, and anauxiliary winding, as generally indicated at A. As shown in FIG. 2, themain winding M of the stator assembly 3 is constituted by two mainwinding coil sets, as indicated at MC1 and MC2. Likewise, the auxiliarywinding A is constituted by two auxiliary coil sets, as indicated at AC1and AC2. Stator assembly 3 illustrated in FIG. 2 is an eighteen poleskein wound winding inserted in the slots of a thirty six slot statorcore 5. Such a skein wound coil set for either the auxiliary or mainwinding may be formed on a skein coil former, such as is disclosed inthe coassigned U.S. Pat. No. 4,357,968, issued to Vernon E. Kiefferwhich is herein incorporated by reference. Additionally, the main coilsets and the auxiliary coil sets are inserted in the slots 11 of core 5in layered groups of coils in the manner is described in the copendingand coassigned U.S. Pat. No. 4,426,771, which is also hereinincorporated by reference. Thus, a detailed disclosure of the manner inwhich the coil sets MC1, MC2, AC1 and AC2 are inserted in the slots 11of core 5 may be had by making reference to the disclosure of thelast-mentioned U.S. Pat. No. 4,426,771. Moreover, while the windingsshown in FIG. 2 were heretofore described as being skein wound coilsets, it will be understood, particularly when reference is had to theabove-mentioned U.S. Pat. No. 4,426,771, that the windings W may beso-called concentric wound coils inserted in the slots of the statorcore in an overlapping insertion pattern in accordance with the methoddescribed in U.S. Pat. No. 4,426,771. It will also be understood thatthe windings W of stator assembly 3 may be skein wound and formed suchthat each of the coils of the coil sets of both the main and auxiliarywindings span an equal number of teeth, such as disclosed in theco-assigned U.S. patent application Ser. No. 471,831 to Stephen M.Breit, which is also herein incorporated by reference.

Referring now to FIGS. 3 and 4, the pattern of the layered groupings ofthe main and auxiliary winding coil sets illustrated in FIG. 2 can bemore easily seen. As heretofore explained, stator assembly 3, as shownin FIG. 3, is an eighteen pole winding inserted in stator core 5 havingthirty-six slots S1-S36 with the windings being inserted in nine layeredgroupings of alternating coils of the auxiliary and main windings A andW so as to constitute the physical poles of the stator with theselayered groupings being substantially equally angularly distributedaround the core. More specifically, the first coil set AC1 of auxiliarywinding A is shown to comprise a plurality (e.g., nine) of seriallyconnected coils, as indicated at AC1a-AC1i. Likewise, the first mainwinding coil set MC1 comprises a plurality (e.g., nine) of seriallyconnected coils, as indicated at MC1a-MC1i. Still further, the secondmain winding coil set MC2 comprises nine serially connected coils, asindicated at MC2a-MC2i, and the second auxiliary coil set AC2 comprisesnine serially connected coils, as indicated at AC2a-AC2i.

As shown in FIG. 4, the main winding coil sets MC1 and MC2 are seriallyconnected and thus form a continuous main winding M. Further, auxiliarywinding coil sets AC1 and AC2 are connected in series with a first tappoint TP1 therebetween connected to a respective leadwire L1 whichextends out of the motor shell, down through wireway 25 for connectionsto the appropriate terminals of selector switch 33 for purposes as willappear. Another or last tap point, as indicated at TP2, is provided atthe opposite end of the second or last auxiliary coil set AC2 and has arespective leadwire L2 connected thereto which extends exteriorily ofthe motor through the wireway for connection to selector switch 33. Apermanent running capacitor, as indicated generally at C, is seriallyconnected to the auxiliary winding A and, together with the auxiliarywinding, is in parallel to main winding M.

As has been previously pointed out, each of the auxiliary winding coilsets AC1 and AC2 comprises a plurality of series connected coils, asindicated at AC1a-AC1i and AC2a-AC2i, respectively. In accordance withthis invention, in the high speed mode of operation, 120 volt ACelectrical power is connected to tap point TP2 via the leadwire L2 suchthat both of the auxiliary winding coil sets AC1 and AC2 together withcapacitor C are connected in parallel with the entire main winding M tothe other power input lead Pl whereby the motor 1 of the presentinvention operates in its high speed mode of operation. When it isdesired to selectively switch the speed of motor 1 from its high speedmode of operation to its slow speed mode of operation, AC electricalpower is removed from the last tap point TP2 and is applied to the firsttap point TP1 via the leadwire L1. In this condition, capacitor C andonly the first auxiliary winding coil set AC1 are connected in parallelto the main winding M. It will be noted that the second auxiliary coilset AC2 is now in series with the main winding M and thus constitutes apart of the main winding. It will be further be noted that in both thehigh and low speed modes of operation, the energized coils of theauxiliary winding (whether only the first auxiliary winding coil set AC1or both of the auxiliary winding coil sets AC1 and AC2 are energized),the coils are uniformly distributed around the stator core 5 atgenerally equal angular intervals so as to result in a balanced fluxfield for the motor which in turn results in quiet operation of themotor. It will also be noted that the speed control system of thepresent invention accomplishes effective speed control in a balancedfashion without the necessity of external inductive reactors, withoutthe requirement of external capacitors, and without the requirement ofadditional intermediate main windings inserted in the slots of thestator core thereby resulting in a considerable savings of materials, ina lower slot fill for the motor, and resulting in a substantial savingsin the amount of copper magnet wire required to form the windings W ofthe motor 1.

Referring now FIGS. 5 and 6, another stator assembly, as generallyindicated at 3', is shown for another embodiment of a motor inaccordance with this invention. It will be understood that the "primed"reference characters in regard to FIGS. 5 and 6 denote parts having acorresponding construction and function to corresponding partsheretofore described in regard to FIGS. 1-4. Generally, the primarydifference between the stator assembly 3, as shown in FIGS. 3 and 4, andthe stator assembly 3', as shown in FIGS. 5 and 6, is that statorassembly 3 is for an eighteen pole, two speed motor whereas the statorassembly 3' is for a twelve pole, two speed motor. In each instance, thestator cores 5 and 5' each include thirty-six radial core slots S1-S36and S1'-S36', respectively Since the construction and operation ofstator 3' is generally similar to stator 3, as heretofore described, adetailed description of the construction and operation of the twelvepole, two speed PSC motor, as illustrated in FIGS. 5 and 6, will not beherein repeated for the sake of brevity.

In FIGS. 7 and 8, still another embodiment of a stator assembly, asindicated at 3", incorporating the speed control system and method ofthe present invention is depicted. Generally, stator assembly 3" isintended for use in a twelve pole, four speed PSC electric inductionmotor. The "double primed" reference characters indicate parts having acorresponding construction and function to corresponding partsheretofore described in regard to the stators 3 and 3' shown in FIGS. 3and 4 and in FIGS. 5 and 6, respectively. A primary difference betweenstator assembly 3" and stator assembly 3' is that the auxiliary windingA" has four auxiliary winding coil sets, as indicated at AC1"-AC4",whereas the auxiliary winding A' of stator 3' only has two auxiliarywinding coil sets AC1' and AC2'. Even more specifically, each of theauxiliary winding coil sets ACl"-AC4" comprises a plurality (e.g., six)of serially connected coils. For example, coil set ACl" includes sixserially connected coils AC1a"-AC1f". The coils of winding W" areinserted in core 5" in layered groupings generally in accordance withthe above-mentioned, coassigned U.S. Pat. No. 4,426,771.

Referring now to FIGS. 9-11A, three different connection patterns forthe twelve pole, four speed windings W", as heretofore described inregard to FIGS. 7 and 8, are illustrated. Referring first to FIGS. 9 and9A, it will be seen that the auxiliary winding A" comprises fourserially connected coil sets ACl"-AC4" in series with permanent runcapacitor C". A first tapping point, as indicated at TP1", is providedbetween auxiliary winding coil sets AC1" and AC2". A second tappingpoint TP2" is provided between the second and third auxiliary coil setsAC2" and AC3", and a third tapping point TP3" is provided between thethird and the fourth auxiliary coil sets AC3" and AC4". Still further, afourth or last tapping point, as indicated at TP4", is provided betweenthe last auxiliary coil set AC4" and main winding M". A multipleposition, single throw, multiple pole speed selector switch, asindicated at 33", is provided and is connected to one of the powerleads, as indicated at P2, of a source of AC electrical power. Switch33" has a selectively movable switch arm SA" selectively movable to anyone of a number of pole positions including an off position in which thewindings W" are de-energized to a high speed position, to a firstintermediate speed position, to a second or slower intermediate speedposition, and to a low speed position. Respective lead wires L4", L3",L2" and Ll" connected the high, first intermediate, second intermediateand low speed terminals of switch 33" to tap points TP4", TP3", TP2" andTP1".

In FIG. 9A, each of the auxiliary winding coil sets ACl"-AC4" is shownto each comprise six serially connected coils, as indicated byAC1a"-AC1f"--AC4a"-AC4f', respectively. Furthermore, the first tappingpoint TP1" is shown to comprise a connection between the first auxiliarycoil set AC1" and the second auxiliary coil set AC2' and the low speedterminal of selector switch 33". The second tapping point TP2" is shownto comprise a connection between both the second and third auxiliarycoil sets AC2" and AC3" and the second intermediate speed switchterminal of selector switch 33". The third tapping point TP3" is shownto comprise a connection between auxiliary coil sets AC3" and AC4" andthe first intermediate selector switch contacts. Likewise, the fourth orlast tapping position TP4" comprises an electrical connection betweenthe fourth auxiliary coil sets AC4" and the main winding and between thehigh speed switch terminal of selector switch 33".

Thus, when switch arm SA" of switch 33" is moved from its off to itshigh speed position (as shown in FIGS. 9 and 9A), AC electrical powerfrom lead P2 is supplied to the last tapping point TP4" thereby toconnect all of the coil sets ACl"-AC4" in series with each other and inseries with capacitor C" and so as to connect the capacitor and all ofthe coil sets in parallel with main winding M" such that the motoroperates at its high speed mode of operation. When switch arm SA" ismoved from its high speed position to its first intermediate operation,AC power from lead P2 is connected to tapping point TP3 such that onlythe first through the third auxiliary coil sets ACl"-AC3" are energizedin series with capacitor C" and such that the first three coil sets areenergized in series with both main winding M" and with the fourthauxiliary coil set AC4" such that the motor operates at its first orhighest intermediate speed mode of operation. When the switch arm SA" ismoved to its second intermediate position, AC electrical power from leadP2 is supplied to the second tapping point TP2" such that only the firstand second auxiliary coil sets AC1" and AC2" are connected in serieswith capacitor C" and such that the last two auxiliary coil sets AC3"and AC4" are connected in series with main winding M" whereby the motoroperates at a still slower intermediate speed of operation. Lastly, whenswitch arm SA" is connected to its low speed terminal, AC electricalpower from lead P2 is supplied to the first tapping point TP1" such thatonly the first auxiliary coil set ACl" is connected in series withcapacitor C" and such that the last three auxiliary coil sets AC2"-AC4"are connected in series with main winding M" whereby the motor operatesat its slow speed mode of operation.

EXAMPLE

A K55 twelve pole PSC ceiling fan motor, such as is illustrated in FIG.7-9A, was assembled in the manner heretofore described. The main windingM" included 285 turns of No. 30 copper magnet wire and the auxiliarywinding A" included 284 turns of No. 30 copper magnet wire, having atotal magnet wire weight of about 1.0 pounds (454 grams). The value ofcapacitor C" was six microfarads, 220 volts. When assembled in anoverhead ceiling fan motor configuration with the paddle fan blades inplace on hub 23, the motor was operated at four different operationalspeeds (i.e., high speed, a first intermediate speed, a secondintermediate speed, and a low speed). The results of the tests for thismotor showing selector switch position, current draw (as expressed inamps), power consumed (expressed in watts), and fan speed (expressed inRPM) are shown below in Table I.

                  TABLE I                                                         ______________________________________                                                 CURRENT                                                              SPEED    DRAW       POWER CONSUMED  SPEED                                     POSITION (AMPS)     (WATTS)         (RPM)                                     ______________________________________                                        High     .66        78              242                                       1st Intermed.                                                                          .50        56              185                                       2nd Intermed.                                                                          .37        38              123                                       Low      .29        28               73                                       ______________________________________                                    

It will be understood that a comparable prior art motor, such as shownin FIG. 12, would require substantially more magnet wire for itswindings.

Referring now to FIGS. 10 and 10A, an alternative lead wire connectionpattern for windings W" inserted in stator core 5" in a manner generallysimilar to that shown in FIG. 7 is illustrated. As best shown in FIG.10, the primary difference between the lead wire connection patternsbetween FIG. 9 and FIG. 10 is that the fourth auxiliary coil set AC4" ofFIG. 10 is not connected in series to main winding M" except when switcharm SA" is in its high speed position. Still further, an on/off switch,as generally indicated at 35, is provided in series with power lead P2so as to control energization and de-energization of windings W". Withon/off switch 35 closed, AC power is supplied to main winding M" and tothe power input terminal 37 speed selector switch 33" by a lead L5".With selector switch arm SA" in its high speed mode of operation, all ofthe auxiliary coil sets ACl"-AC4" are connected in series with oneanother and in series with capacitor C", and further all of theauxiliary coil sets and the capacitor are connected in parallel withmain winding M" such that the motor illustrated in FIG. 10 operates inmuch the same manner as the motor illustrated in FIG. 9 in its highspeed mode of operation. However, when the selector switch SA" of themotor of FIG. 10 is moved from its high speed position to its firstintermediate speed position, to its second intermediate speed position,or to its slow speed position, one or more of the auxiliary coil setsAC4", AC3" and/or AC2" is removed from the auxiliary winding circuitsuch that when AC power from lead P2 is supplied to tapping pointsTPl"-TP3", the removed auxiliary coil sets are not placed in series withmain winding M", but rather are de-energized. It will be appreciatedthat this is a different mode of operation than in the voltage dividerembodiment shown in FIGS. 9 and 9A which when one of the slower speedmodes of operation is utilized, one or more of the auxiliary coil setsis connected in series with the main winding and thus constitutes aportion of the main winding.

Referring now to FIGS. 11 and 11A, still another connection pattern forthe auxiliary winding A" is illustrated in which the speed selectorswitch, as indicated at 33a", is shown to be a four position speedselector switch (whereas the four speed selector switches 33" shown inFIGS. 9-10A was a five position switch) and yet four different speeds ofoperation may yet be controlled by means of the three speed selectorswitch 33a". More specifically, in FIG. 11, it will be noted that tappoints TPl"-TP4" are generally similar to the tap points heretoforeillustrated and described in regard to FIG. 9 However, a separate on/offswitch 35, such as heretofore described in regard to FIGS. 10 and 10A,is interposed in power input lead P2. Still further, a power lead, asindicated at L5", interconnects tapping point TP4" (which is directlyconnected to power lead TP2 when on/off switch 35 is closed) and theinput terminal 37 to speed selector 33a". Thus, when the four positionspeed selector switch 33a" is in its open or off position and whenon/off switch 35 is closed, AC electrical power is supplied to tappingpoint TP4" such that the windings W" of FIG. 11 operate in a high speedmode of operation generally similar to the high speed mode of operationheretofore described in regard to both FIGS. 9 and 10. That is, in thehigh speed mode of operation, all of the auxiliary coil sets ACl"-AC4"are connected in series with capacitor C" and the auxiliary winding A"and the capacitor C" are in parallel with main winding M". However, uponmoving the selector switch arm SAa" from its high speed position to oneof its intermediate speed positions or to its low speed position, one ormore of the auxiliary coil sets of the auxiliary winding are shorted outand thus the motor operates in a slower speed mode of operation. Thus,with the winding and switch configurations as shown in FIGS. 11 and 11a,four speeds of operation may be achieved utilizing a three operationalspeed speed selector switch 33a". It will be further understood thatwhen one or more of the auxiliary coil sets AC2"-AC4" of the windingsshown in FIGS. 11 and 11A are shorted out, so-called circulatingcurrents will exist in the shorted auxiliary coil sets which may causelosses in these shorted coil sets which will, to some degree, reduce theoperating efficiency of the motor. However, in certain motorapplications, such as overhead ceiling fan applications in which thecurrent draw for the motor is relatively low, such a motor, even withthese inefficiencies, still has a satisfactory operating efficiency anddoes not result in excessive heating of the windings of the motor, evenduring prolonged operation of the motor at its slower speeds ofoperation.

Generally, the motor and method of this invention, as above-described,utilizes the auxiliary winding coil sets, which may be selectivelyenergized in a predetermined manner, to vary the effective turn ratiobetween the auxiliary winding A and the main winding M. At higher speedmodes of operation, the effective turn ratio is maximized and the motoroperates at its higher speed mode of operation, while at low speed, asignificant portion of the auxiliary winding is effectively removed (orplaced in series with the main winding) thus reducing the effective turnratio and the speed of the motor.

Referring now to FIG. 12, a prior art tapped winding PSC motor is shownutilizing three intermediate main windings, as indicated at M1-M3,connected in series with its main winding M. The auxiliary winding Atogether with the permanent capacitor C are connected in series with itsmain winding M. In its high speed mode of operation, electrical power issupplied between power lead Pl and the high speed switch position, asshown in FIG. 12, such that none of the intermediate main windings M1-M3is energized in series with the main winding M thereby to permit themotor to operate in its high speed mode of operation However, when thespeed selector switch applies AC electrical power to the low speedswitch point, as shown in FIG. 12, all three of the intermediate mainwindings M1-M3 are connected in series to the main winding M such thatthe voltage across the main winding is significantly reduced and suchthat the motor will operate at a slower speed mode of operation.

In FIG. 13, a motor generally analogous to the motor shown and describedin regard to FIGS. 9 and 9A is depicted which, like the prior art tappedwinding motor shown in FIG. 12, has four different operating speeds.However, it will be noted that the motor of the present invention (asshown in FIG. 13) only has two windings, that is main winding M" andauxiliary winding A". More specifically, the intermediate main windingsM1-M3 of the prior art tapped winding motor of FIG. 12 have beeneliminated, and yet the motor of the present invention, as shown in FIG.13, has the same number of speeds as the prior art motor of FIG. 12.Surprisingly, however, the motor of the present invention as shown inFIG. 2 results in a substantial savings of copper windings due to thefact that the intermediate main windings M1-M3 of the motor can beeliminated. It has been found that for two speed motors made inaccordance with this invention having substantially the same poweroutput and the same speed range as similar prior art tapped windingmotors (such as shown in FIG. 12) can result in a minimum savings ofabout twenty percent (20%) of copper magnet wire in the windings.However, if a multiple speed motor of the present invention and of theprior art having three or more speeds are compared, such motors made inaccordance with this invention would result in even more substantialmaterial savings. Those skilled in the art will recognize that thisrepresents a significant cost savings. Moreover, the main and auxiliarywindings of the motor of the present invention are easier to fabricateand to insert in the slots of the stator core due to the fact that theintermediate main windings have been omitted. Also, the motor of thepresent invention results in a lower slot fill. More specifically, "slotfill" is a term of art which is a ratio (expressed as a percentage) ofthe cross-sectional area of the slots 11 of core 5 filled by thewindings W inserted therein and the total available cross sectional areaof the slots. Motors made in accordance with the present invention havein slot fill reductions of at least 32%, compared with comparable priorart motors.

Referring now to the alternative embodiment of the multiple speed motorof the present invention shown in FIG. 14, the motor is shown tocomprise a main winding, as generally indicated at MN, having two mainwinding coil sets MN1 and MN2, respectively. These main winding coilsets are spaced at substantially equal angular intervals around thestator such that the main winding is balanced within the stator.Additionally, the windings of this motor comprise an auxiliary winding,as generally indicated at AUX, having four auxiliary winding coil sets,AUX1-AUX4, which are also distributed at equal angular intervals aroundthe stator, such that the auxiliary winding AUX is physically balancedwithin the stator. A running capacitor, as generally indicated at CAP,is parallel connected, as indicated at A, to one side of main windingMN, which in turn is connected to one side L1 of an alternating currentpower source. The other side of capacitor CAP is connected in series toauxiliary winding coil set AUX4. Further, all of the auxiliary windingcoil sets AUX1-AUX4 are serially connected to one another, and have tappoints TAP1-TAP4 therebetween.

As mentioned, one end of main winding MN is connected to a first powerlead L1 of an alternating current power source, and the other end of themain winding is connected to the selector arm SA of a four-positionspeed selector switch, as generally indicated at 33. The speed selectorswitch has four terminals engagable by switch arm SA, with the firstswitch terminal 1 being connected to one end of auxiliary coil set AUX1at TAP1, and to a second line L2 of the alternating current powersource, as indicated at B. The second switch terminal is connected totap point TAP2 between auxiliary coil sets AUX1 and AUX2. The thirdswitch terminal is connected to tap point TAP3 between auxiliary windingcoil sets AUX2 and AUX3. The fourth speed selector switch terminal isconnected to tap point TAP4 between auxiliary coil sets AUX3 and AUX4.An on/off switch S2 is provided in line L2 for energization andde-energization of the motor. It will be understood that in certainapplications, such as in the blower motor of a furnace or the like,switch S2 may be controlled by the thermostat for the furnace, while inother applications, such as overhead ceiling fans, a separate on/offswitch, separate from switch 33, may be required to selectively energizeand de-energize the motor. Alternatively, a double pull switch (notshown) may be provided.

In operation with on/off switch S2 closed, and with switch arm SA ofspeed selector switch 33 in its first or high speed position, as shownin FIG. 14, switch arm SA is engageable with the first terminal of thespeed selector switch such that all of the auxiliary winding coil setsAUX1-AUX4 are connected in series with capacitor CAP, and the entireauxiliary winding AUX and the capacitor are connected in parallel toboth main winding coil sets MN1 and MN2. Thus, the motor operates in itshigh speed mode of operation. If speed selector switch arm SA is movedfrom its high speed position to a first intermediate speed such that theswitch arm is in contact with the second switch terminal, then auxiliarywinding coil sets AUX2-AUX4 and capacitor CAP are connected in parallelto main winding MN, and the capacitor, auxilary coil sets AUX2-AUX4, andmain winding MN is connected in series to auxiliary coil set AUX1 andthe other lead L2 of the power source such that the motor operates at afirst intermediate speed. With the switch selector arm SA3 moved intocontact with the third switch terminal, auxiliary winding coil sets AUX3and AUX4 are connected in series to the capacitor, and these last twomentioned auxiliary winding coil sets and the capacitor are in parallelwith the main winding MN. Thus, the main winding, auxiliary winding coilset AUX3 and AUX4, and the capacitor are in series connection with thesecond power lead L2 and with auxiliary winding coil sets AUX1 and AUX2such that the motor operates at a slower intermediate speed. Finally,with switch arm SA4 positioned to be in contact with the fourth or lowspeed switch terminal, auxiliary winding coil sets AUX4 and thecapacitor are connected in parallel to main winding MN, and auxiliarywinding coil set AUX4, the capacitor, and the main winding are connectedin series to the second power lead L2 and to auxiliary coil setsAUX1-AUX3 such that the motor operates at its slowest speed mode ofoperation. Of course, it will be realized that the number of coil setsin auxiliary winding AUX may be varied so that the motor may have anydesired number of operational speeds.

In the embodiments of the present invention shown in FIGS. 1-13, it willbe appreciated that the auxiliary windings of these motors remain inparallel connection with the ends of the main windings, and voltagesapplied to the taps within the auxiliary windings achieve differentspeeds of operation of the motor. In contrast, the motor of FIG. 14 hasthe ends of the entire main winding MN serially connected to differenttaps within the auxiliary winding AUX via switch 33 so as to achieve thedifferent speeds of operation while one side of the line voltage of thealternating current source (i.e., L2) remains connected to one end ofthe auxiliary winding In essence, this changes the type of connectionfor the motor from a so-called "L-connection" motor to a so-called"T-connection" motor.

Further, with the motors shown in FIGS. 1-13, it will be appreciatedthat in the event the running capacitor of the motor fails in a shortedcondition when the motor is in its low speed mode of operation, all ofthe line voltage will be applied to only one coil set of the auxiliarywinding. Since this one coil set of the auxiliary winding will have arelatively low resistance, and since the full line voltage is appliedthereto, this can result in an extremely rapid resistance heating of theone auxiliary winding leading to rapid damage or failure of the motorwindings. In an effort to prevent this condition from occurring, someapplications require the provision of a rapid acting thermal protectivedevice to be incorporated within the auxiliary winding. These rapidacting thermal protector devices are difficult to obtain in commercialquantities, and are relatively expensive, as compared with conventionalthermal protectors.

Those skilled in the art will appreciate that the tapped section of theauxiliary winding of the motor shown in FIG. 14 is, in all speeds ofoperation, connected serially to the main winding, and thus the mainwinding acts like a voltage dropping resistor, and eliminates therequirement of a rapid-acting thermal protector. Thus, even though someapplications of the present invention may require a separate on/offswitch S2, or a double pull switch (not shown) incorporating both thespeed control switch SA and the on/off switch S2, an important netsavings in component costs may nevertheless be realized with the motorof the present invention. It will also be appreciated that while switch33 has been described as an adjustable speed selector switch, such as apull chain switch readily operable by a user to change motor speeds,switch 33 could be a switch only intended to be adjusted by a fieldinstallation person for presetting the operational speeds of a motor.For example, in a blower motor application in a residential forced airfurnace, the installation person may select the desired operationalspeed of the blower motor, depending on duct parameters and the like,and then open up the switch housing and manually set switch arm SA so asto best approximate the desired operation of the blower.

As with motors described above, the motor of FIG. 14 always operates, inall modes of operation, in a balanced fashion so that the energizedwindings are uniformly distributed around the stator, regardless of thespeed of operation selected.

In view of the above, it will be seen that the other objects of thisinvention are achieved and other advantageous results obtained.

As various changes could be made in the above constructions or methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawing shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. In a multiple speed electric induction motorcomprising: a stator having windings; and a rotor rotatable with respectto said stator; said windings comprising a main winding and an auxiliarywinding, wherein the improvement comprises:a capacitor, one side ofwhich is serially connected to said auxiliary winding; said auxiliarywinding comprising a plurality of serially connected coil sets,including a first and a last coil set, with each coil set having aplurality of serially connected within said auxiliary winding betweencoil sets thereof, wherein the method of this invention comprises thesteps of: inserting the coils of each of said coil sets of saidauxiliary winding and of said main winding in said slots at equalangular intervals around said core; connecting one side of a source ofalternating electrical current to one side of said main winding and tosaid capacitor, and connecting the other side of said power source tosaid auxiliary winding; then, to operate said motor at a high speed modeof operation, connecting said main winding to said auxiliary windingsuch that all of the coil sets of said auxiliary winding are energizedin series with said capacitor and such that all of said auxiliarywinding coil sets and said capacitor are in parallel with said mainwinding and then, to operate said motor at a slower speed mode ofoperation, connecting said main winding to said first tap point withinsaid auxiliary winding such that only a portion of said auxiliarywinding coil sets is energized in series with said capacitor, such thatsaid portion of said auxiliary winding coil sets and said capacitor arein parallel with said main winding, and such that the remaining coilsets of said auxiliary winding are connected in series to saidcapacitor, to said portion of said auxiliary winding coil sets, and tosaid main winding such that in the event of said capacitor fails in theshorted condition, said main winding acts as an impedence drop limitingcoils so as to constitute the poles of said winding; a first tap pointbetween said first and last coil sets of said auxiliary winding; andswitch means for a high speed position in which a maximum number of saidcoil sets of said auxiliary winding is energized in series with saidcapacitor and in which said maximum number of said coil sets of saidauxiliary winding and said capacitor are in parallel with said mainwinding, for a low speed position in which a minimum number of said coilsets of said auxiliary winding is energized in series with saidcapacitor and in which said minimum number of coil sets of saidauxiliary winding and said capacitor are in parallel with said mainwinding and said minimum number of coil sets of said auxiliary windingare in series with the remaining coil sets of said auxiliary winding andfor connecting said main winding and said remaining coil sets of saidauxiliary winding when in said low speed position so as to act as avoltage dropping means for said minimum number of coil sets of saidauxiliary winding in the event said capacitor fails in a shorted mode.2. A multiple speed electric induction motor comprising:a stator; arotor rotatable with respect to said stator; windings associated withsaid stator, said windings comprising a main winding and an auxiliarywinding; a capacitor, one side of which is serially connected to saidauxiliary winding; said auxiliary winding comprising a plurality ofserially connected coil sets, including a first and a last coil set,with each coil set having a plurality of serially connected coils atsubstantially equal angular intervals around a central bore so as toconstitute the poles of said winding; a first tap point between saidfirst and last coil sets of said auxiliary winding; a pair of powerlines connected to a source of alternating current power, one side ofsaid main winding and the other side of said capacitor being connectedto one side of said power source and the other side of said auxiliarywinding opposite said capacitor being connected to the other side ofsaid power source; and a speed selector switch having a movable switchmember connected to the other side of said main winding, said switchmember being movable between a high speed position in which a maximumnumber of said coil sets of said auxiliary winding is connected inseries with said capacitor, and in which said maximum number of coilsets of said auxiliary winding and said capacitor are in parallel withsaid main winding, and a low speed position in which a minimum number ofcoil sets of said auxiliary winding is connected in series with saidcapacitor and in which said minimum number of auxiliary coil sets andsaid capacitor are in series with the remaining coil sets of saidauxiliary winding, said speed selector switch constituting means forconnecting said main winding and said remaining coil sets of saidauxiliary winding so as to protect said minimum number of auxiliary coilsets in the event said capacitor fails in a shorted condition.
 3. Amultiple speed electric induction motor comprising:a stator; a rotorrotatable with respect to said stator; windings associated with saidstator, said windings comprising a main winding and an auxiliarywinding; a capacitor, one side of which is serially connected to saidauxiliary winding; said auxiliary winding comprising a plurality ofserially connected coil sets, including a first and a last coil set,with each coil set having a plurality of serially connected coils atsubstantially equal angular intervals around a central bore so as toconstitute the poles of said winding; a first tap point between saidfirst and last coil sets of said auxiliary winding; a pair of powerlines connected to a source of alternating current power, one side ofsaid main winding and the other side of said capacitor being connectedto one side of said power source and the other side of said auxiliarywinding opposite said capacitor being connected to the other side ofsaid power source; and a speed selector switch having a movable switchmember connected to the other side of said main winding, said switchmember being movable between a high speed position in which a maximumnumber of said coil sets of said auxiliary winding is connected inseries with said capacitor and in which said maximum number of coil setsof said auxiliary winding and said capacitor are in parallel with saidmain winding, and a lower speed position in which a minimum number ofcoil sets of said auxiliary winding is connected in series with saidcapacitor and in which said minimum number of auxiliary coil sets andsaid capacitor are in parallel with said main winding and said minimumnumber of auxiliary coil sets is in series with the other coil sets ofsaid auxiliary winding, said switch constituting means for connectingsaid main winding and said remaining auxiliary winding coil sets so asto act as a voltage dropping means and for protecting said minimumnumber of auxiliary winding coil sets in the event said capacitor failsin a shorted condition.
 4. A method of controlling the speed of amultiple speed motor and protecting at least a portion of the windingsof the motor against excessive resistance overheating without the use ofa thermal protector, said motor comprising a stator, a rotor, andwindings associated with said stator, said windings comprising a mainwinding and an auxiliary winding, a capacitor in series with saidauxiliary winding, each of said windings having a plurality of polesplaced in a stator core at substantially equal angular intervalstherearound, said auxiliary winding comprising a plurality of coil sets,each having a plurality of serially connected coils, and a first tappoint within said auxiliary winding between coil sets thereof, whereinthe method of this invention comprises the steps of:inserting the coilsof each of said coil sets of said auxiliary winding and of said mainwinding in slots at equal angular intervals around said core; connectingone side of a source of alternating electrical current to one side ofsaid main winding and to said capacitor, and connecting the other sideof said power source to said auxiliary winding; then, to operate saidmotor at a high speed mode of operation, connecting said main winding tosaid auxiliary winding such that all of the coil sets of said auxiliarywinding are energized in series with said capacitor and such that all ofsaid auxiliary winding coil sets and said capacitor are in parallel withsaid main winding and then, to operate said motor at a slower speed modeof operation, connecting said main winding to said first tap pointwithin said auxiliary winding such that only a portion of said auxiliarywinding coil sets is energized in series with said capacitor, such thatsaid portion of said auxiliary winding coil sets and said capacitor arein parallel with said main winding, and such that the remaining coilsets of said auxiliary winding are connected in series to saidcapacitor, to said portion of said auxiliary winding coil sets, and tosaid main winding such that in the event of said capacitor fails in theshorted condition, said main winding acts as an impedance drop limitingthe flow of current through said portion of said auxiliary winding coilsets, and such that the flux of the motor is balanced when said motoroperates at its slower speed mode of operation.